How do muscle cells generate force and movement through the interaction of actin and myosin filaments?

Muscles are responsible for generating force and movement in the body. The fundamental mechanism behind muscle contraction involves the interaction between two types of protein filaments: actin and myosin. Actin is a thin filament while myosin is a thick filament, and they work together to cause muscle contraction.

When a muscle is stimulated, calcium ions are released from the sarcoplasmic reticulum, a network of membranes found in muscle fibers. The calcium ions bind to a protein called troponin, which is located on the actin filaments. This binding causes a conformational change in troponin, which in turn moves tropomyosin, another protein found on actin, away from the myosin binding site on actin.

With the binding site exposed, the myosin head, which has ATP (adenosine triphosphate) attached to it, binds to the actin filament. This binding causes a release of the ATP and a conformational change in the myosin head, which causes the myosin head to pull on the actin filament, moving it towards the center of the sarcomere, the basic unit of muscle contraction.

As the myosin head pulls on the actin filament, ADP (adenosine diphosphate) and phosphate are released from the myosin head, causing it to detach from the actin filament. The myosin head then re-cocks, allowing it to bind to another actin filament, and the process repeats itself, resulting in muscle contraction.

This process of actin and myosin filament interaction is repeated in muscle fibers throughout the body, allowing us to perform a wide range of movements.